ubicloud/bin/restarter

#!/usr/bin/env ruby
# frozen_string_literal: true

minimum_time_alive = Integer(ENV.fetch("RESTART_MINIMUM_TIME_ALIVE", "3600"), 10)
require "json"

command = ARGV.dup.freeze
start_time = Time.now
shutting_down = false

iso_start = start_time.utc.strftime("%Y-%m-%dT%H:%M:%S%:z").freeze
puts JSON.generate(restarter: {
  start_time: iso_start,
  startup: {
    command:,
    minimum_time_alive:
  }
})

loop do
  pid = Process.spawn(*command)
  Signal.trap("TERM") do
    Process.kill(:TERM, pid)
    shutting_down = true
  end
  Process.wait(pid)
  status = $?

  # Extra newline to prevent blending with subprocess just in
  # case. Done as a separate system call, to be extra-accommodating to
  # loggers that may want process things one system call at a time:
  # below PIPE_BUF each write() matches with a read().
  puts

  puts JSON.generate(restarter: {
    start_time: iso_start,
    command_exit: {
      command:,
      exitstatus: status.exitstatus,
      pid: status.pid,
      success: status.success?
    }
  })
  exit status.exitstatus if shutting_down

  sleep(rand(1..10))

  if Time.now - start_time > minimum_time_alive
    puts JSON.generate(restarter: {start_time: iso_start,
                                   shutdown: {
                                     command:,
                                     minimum_time_alive:
                                   }})
    exit
  end
end